Integrated sustainable process for polyhydroxyalkanoates production from lignocellulosic waste by purple phototrophic bacteria

Abstract

Purple phototrophic bacteria (PPB) showed an enormous potential for polyhydroxyalkanoates (PHA) production using the hydrolysate from lignocellulosic waste as feedstock. Thermal hydrolysis pretreatment was carried out at three different temperatures (120, 150, and 180°C) aiming to improve the biodegradability of the lignocellulosic waste. After this pretreatment, two streams are collected: a solid and a liquid fraction. The anaerobic digestion process of the pretreated solid fraction at 180°C increased its biodegradability extent by 31% compared to the untreated biomass, yielding 210 ± 10 L CH4 kg−1 VS even when the liquid fraction was removed. On the photoheterotrophic of the liquid fraction, PPB were able to remove up to 55% of COD during batch operation, showing peaks of PHA production yield up to 21 wt.%. The treatment of the liquid fraction obtained at high temperatures (T ˃ 120°C) reduces biomass growth and COD consumption efficiency, and thus potential productivity, with no effect over the specific activity and the biomass yield, indicating growth limitation by lack of nutrients (N and P). A preliminary economical assessment indicates suitable economic viability based on an energetic autarchy process. This study pioneered a PPB-based biorefinery for PHA production from lignocellulosic residues and aligned within the bioeconomy strategy of the European Union.